It has long been a practice to provide aircraft wings with leading edge and trailing edge devices which are mounted to a fixed wing structure. In the cruise configuration, these leading and trailing edge devices are in retracted position to provide with the fixed wing an optimized aerodynamic configuration.
For take-off and climb, these leading and trailing edge devices are generally moved toward intermediate positions which optimize performance of the wing during the take-off and climb, where improved lift performance is needed, but drag still needs to be kept within reasonable limits. The third operating configuration is the high lift position, where the leading and trailing edge devices are fully deployed to provide adequate lift at relatively low speeds. This high lift configuration is commonly used when the aircraft is landing.
Leading edge devices are commonly in the forms of slats which in the cruise configuration conceal the forward and upper forward surface portion of the wing, with the leading edge of the slat forming the leading edge of the wing/slat combination in cruise configuration. The trailing edge of the leading edge slat is positioned immediately adjacent to the upper surface of the fixed wing so that it forms, as much as possible, a continuous upper aerodynamic surface for the slat/wing combination in the cruise configuration.
In the take-off and climb configuration, the slat is moved forward to an intermediate location to extend the effective cord length of the wing, and is also generally angled downwardly to some extent to increase the camber of the wing. In some instances, it is desirable to have the trailing edge of the slat be positioned to be in contact with the upper forward fixed wing surface portion to form a continuous upper aerodynamic surface of the slat/wing combination. However, in some arrangements a slot is formed between the slat and the forward portion of the fixed wing in the take-off position.
In the high lift configuration, the slat is generally moved further forwardly from the takeoff and climb position so that the slat has a yet greater downward slant so as to increase the camber of the slat/wing combination, and also so that the slat forms with the fixed wing an aerodynamic slot which results in airflow from beneath the slat upwardly through the slot and over the upper forward surface portion of the fixed wing.
For at least the past three decades, one common way for providing leading edge slat assemblies has been to use an arcuately shaped carrier track that moves along its length in a circularly curved arcuate path from the cruise position, through the intermediate take-off and climb position to the high lift landing position. Among the aircraft which have used and still use this particular arrangement for the leading edge slat are the Boeing 727, 737, 757 and 767.
Such slat assemblies comprise a main arcuately shaped carrier track having a forward end to which the slat is pivotally mounted, with this carrier track moving in an arcuate path between rollers that maintain the travel of the carrier track along this fixed arcuate path. In the earlier 727 configuration, the slat was fixedly attached to the carrier track and formed a slat or gap with the fixed wing at both the takeoff and climb position and also in the high-lift landing position. In the later 737, 757 and 767 configurations in addition to the carrier track, there was provided an auxiliary track subassembly where there is a moveable arm member having its forward end fixedly attached to the slat, with the rear end of the arm member being positioned in a contoured groove of a stationary guide member.
In the 737, 757 and 767, as the slat moves from the cruise position to the intermediate takeoff position, the carrier track is arranged so that the trailing edge of the slat is in engagement with (or at least in close proximity to) the fixed wing upper leading edge surface portion. However, for the high lift landing configuration, in order to properly position the slat to optimize performance relative to lift and other characteristics at the slower speed, the slat needs to be rotated to a position that requires angular movement of the slat relative to the carrier track. This is accomplished by arranging the groove in which the rear end of the positioning arm travels so that it slants in a more forward direction to cause the trailing edge of the slat to tilt further upwardly as the slat is carried further forwardly and downwardly to its high lift position.
Over the years, there have been various improvements or proposed alternative designs in this particular type of leading edge slat assembly. Two of these are shown in patents assigned to The Boeing Company, one being U.S. Pat. No. 4,471,928 (Cole), which discloses an improved configuration for the carrier track, where the carrier track is a slotted I beam defining a U shaped slot along its lower length. A gear rack is mounted within the carrier track slot and a pinion gear meshes with the gear rack to move the carrier track along its arcuate lengthwise axis. The other is U.S. Pat. No. 4,469,297 (Cole) which has the same basic arrangement of a carrier track, bun to drive the track member there is a cable and drum arrangement. The cable extends around the drum, with the ends of the cable being attacked to forward and rear ends of the carrier track.